Most Canadians would love the idea of states joining us
Nope. Not true.
They wouldn't even refuse solidly red states, I think
I would. They would view us as an occupying power, and would be right to think so. Think of Quebec, but instead of being French they're just racist. I don't want that in my Canada.
It would make Canada stronger, and a better life for the states
It would be a clusterfuck. Not Canada's problem to make life better for Americans. Ever heard the saying, people get the government they deserve? Majority of them are assholes or unable to help themselves. If they want to enjoy a better life the Canadian way, they can work on immigrating here. Canada is not an expansionist country. Plenty Happy as is, geopolitically speaking.
Economic power together is enhanced
We've been doing this already, as two separate sovereign nations. Assholes turned it against us. You know, you read the news.
Canada even as 10 states instead of 1, doesn't work because US debt is too high, and US simply has too harsh of a society meant for oligarchy.
Not sure what you're going on about with the US debt. But that alone is a reason for us to not join together. Who the hell would want to inherent that problem? Canadians would be taxed like crazy to help pay that off. If by too harsh of a society, you mean ruthless individualism at the expense of the overall social fabric, which has a nasty effect of creating oligarchs? Correct.
Healthcare would be a major issue.
It would be, but in this scenario is would ironically be the least problematic thing.
These opinions are presented to you by a dual citizen Canadian currently living in the Southeast of America. No normal people here want to invade Canada, and no Canadian wants to be a "savior" of poor abused American states. I'm down to let more people immigrate and become PR or citizens, but not a blanket annexation of entire states. If Americans have a issue with their current federal government, they can take some bricks and throw them through select politicians windows while doing mass strikes like the rest of the civilized world does to keep their democracy clean. The French revolution wasn't bloodless, nor was the American Revolutionary War. Tyrants don't go away on their own.
You know nothing about Canadians nor what the average American thinks and it shows.