This is a big discussion, but I will try to keep it short, and may do another post on this topic later on.
As usual, I'd like to examine the numbers. Congress in particular. The bad news is Canada won't have 2 Senators like every other state. The reason is simple; Canada is a federation. We already have a set of sub-national units that exist within a federal system, they are called Provinces, and it only makes sense that each Province would become it's own State. There may be some issues with some states; PEI for example will be very very small, but even Newfoundland can compete in terms of population with Wyoming. As such, each Province would have 2 Senators. They would be elected the same as other Senators are.
In terms of the house, most provinces are rather small. The Atlantic Provinces would each have 1, while Manitoba and Saskatchewan should just be able to edge into qualifying for 2. The other provinces are more difficult to calculate.
Alberta has 4.23 million people, BC has 4.71, Quebec has 8.29, and Ontario has 13.87
The nearest state to Alberta in terms of population is Kentucky at 4.43 million, it has 6 congressmen in the house, and so Alberta would be assigned 6. The nearest state to BC is either Louisiana or Alabama, the latter has 7 congressmen, so BC would get 7. Ontario is closest to Illinois, at 18, which has 12.86, but that's quite a bit lower. In general there are 1 congressmen for every 650K or so people, so Ontario would get 19. Quebec meanwhile is very close in population to Virginia, at 8.38, and would get 11. Presuming, of course, they stick with this new nation. This is also a very quick and rough way to estimate these numbers, numbers which would change at the first census as the total number is fixed to 435, and as such, adding new states means existing states lose congressmen.
In the coming Federal election, polls show that all 10 provinces would vote for Clinton, even Alberta, so we can presume that's fairly safe. In the Atlantic it's a near certainty that the Democrats would sweep all 4 seats. Manitoba would be split in two, likely Winnipeg and Not-Winnipeg. The former is solidly Democratic, while the latter should also lean towards the Democrats, as Manitoba's rural areas are not as right-wing as in some other provinces.
BC would have 7 new seats; it has 42 seats currently in our house. That means 6 ridings per seat. It's pretty easy to find a 6 seat geographic area of BC that would vote right-wing; it's more difficult to find another 6 seat region. If you gerrymander, you should be able to do it, but the way the geography works, and the way current politics are in the US, it's quite clear to me that this would return 6 Democrats, and likely, 1 Republican from the northern and interior areas.
Ontario would also have 6 riding sized districts. Unlike BC, Ontario has less of a history of voting for "extreme" right-wing parties, and is much more strongly opposed to some Republican ideas, especially with the current set of hot button issues, such as abortion. There should be easily 4 or 5 ridings that could go Conservative, but how many would go Republican? My guess is 4 of those, including to my own dismay, the one including the area I live in. Keep in mind as well that Canada would be "new" to US politics, and as such, the Presidential candidates would likely have a much higher impact on how people vote. As well, 50% of Canadians back the Liberal Party at this time, and that would almost certainly be translated directly into Democratic votes.
Quebec would have seats the size of 7.5 current ridings. Due to the unique politics of Quebec I could see 3 seats going to the Bloc, and possibly some to the Republicans; however, I don't think Quebec will bother sticking around, and so, I will ignore them.
All of the above provinces would produce 2 Democrats as Senators. The only way a Republican could win is if a "big star" ran, such as Micheal Chong, but people like this would probably either run as a Democrat, or change to another level of politics. Additionally, the Democrats are likely to put up their own "big names" for Senator positions such as Chrystia Freeland.
Saskatchewan is where we begin to get into possible Republicans getting elected in a large way. Both seats would be tossups. The seats would likely centre around Regina and Saskatoon. It's very likely the provincial Saskatchewan Party would affiliate with the Republicans, and I do think that this would be enough to push both seats towards the GOP. Despite that, I could still see the Democrats winning at least one of the Senate seats; likely a big-wig like Ralph Goodale, while the other could well go Republican.
Alberta is more complicated. The seats would be about 5 and a half ridings in size. Calgary and Edmonton would each have two seats, which would also include suburban towns around the cities. The two rural seats would nearly certainly go Republican. Calgary's southern seat would almost certainly for Republican as well. The other 3 seats are likely to go Democrat. Despite that, it's quite likely Alberta would return 2 Republican Senators. There are simply more "big names" on the right than there are on the left, and especially if folks like Stephen Harper could be called out of retirement, we'd easily see victories here.
The end result of our little test is that Quebec leaves, while the remainder of Canada elects the following.
58 EVs - Clinton
0 EVs - Trump
In 2014, the Republicans won 247 seats in the House, while the Democrats won 186. This means that our contribution would not change the partisan makeup of the house. However, in the Senate, we have 46 Democrats vs 54 Republicans. Our new totals would be 61 Democrats vs 57 Republicans, a massive change. Given our tendency (if polls are correct) to prefer Democratic candidates for President, it's quite likely that adding Canada to the US would ensure the current balance of power; with a Democratic administration and a Democratic controlled Senate, would continue, while little would be done to turn the House over to Republican control.