This is a complex topic because as you've so rightly mentioned it's very multi-dimensional so it matters a lot what your top priorities are. Let's start with the basics:

1. As a Canadian co-owner of a US corporation you're going to get screwed on taxes. First the US has the highest corporate taxes in the world so you'll be nailed with those, then you've got US dividend withholding taxes to deal with and finally Canadian taxation.

2. You don't have to choose between Canada or the US you could potentially choose somewhere else entirely. People tend only to think of the places where they are involved but as soon as you cross borders the whole world opens up to you.

All of this being said it is highly likely a portion of the income is going to be taxable in the US regardless and Canada regardless because you don't just get taxed based on where you're incorporated you also get taxed based on where you've got a "permanent establishment" and managers and sales people among others are considered "permanent establishments" under the terms of the tax treaty.

Usually, if you've got sufficient scale the best approach in these cases isn't to form just one company but multiple and if you do it well you could actually end up with an incredibly favorable tax position over being based in just one or the other. That being said this takes extra cost and administration so if you're just getting started and not making much money it doesn't make sense.

If you're raising money from Silicon Valley VCs you've essentially got just two choices that are worth considering, a Delaware or California company but this is where sometimes you can use a hybrid structure to get the best of both worlds.

Feel free to contact me if you'd like to discuss details.