I'm Canadian, so I'll give you a one off overview. I'm assuming you are American, so revise this if you are not.
If you are high on lifestyle and lean left in your politics and feel weird when there is no snow on Christmas, you'll more than likely love Canada. Nothing up here will compare to the startup scenes in the SV and such, but if you stick with the bigger cities (Toronto, Vancouver, and Montreal) you'll most likely find enough for you to live with. There are other tech centres like Ottawa, Waterloo and Calgary, but these would be smaller, albeit with the pluses of a smaller city as well.
In general, you need to accept snow and cold in the winter. Places like Toronto can be 50/50 and a lot like say, NYC or Chicago, but Montreal and god forbid the Parries are a guaranteed frozen for 4 months of the year at least. The only real respite from this is the BC coast, but instead of snow you will see 4 months of rain.
You might feel taxed a little bit, but that should only last until you realize that those taxes include all those Health care expenses you no longer need to worry about.
You'll need to accept that Canada is very accepting of its immigrants - almost too much so - and it will be expected that you are as well. Strong Christian right views that compose half of the spectrum in the US will often just not be tolerated here. This is probably the biggest difference between the two countries - your religion and beliefs are personal matters. You will quickly learn about all other countries and cultures from Canada, as there are large communities from the East, Europe, and the Middle East that are encouraged to engage and build the country but to also retain their own differences.
Canada can be VERY different depending on what area you choose to live in, so I'd strongly suggest you look at a few areas and then visit first. Montreal and Vancouver may look similar in size and economy, but they are ridiculously different in many more important ways. Much more so than say Boston compared to Seattle. Pay a lot of attention to this.
I've lived in 4 provinces and visited all the provinces and territories spare the Maritimes. I'll reply if you need any more information about a particular area.
Good luck to you.