No? If I started a company in Canada tomorrow, why would I reduce my talent pool and not look at the US? Most startups are eschewing offices in an obvious move for cash-strapped businesses. If you're hiring remote then borders should be a mild nuisance at worst, and at best a force multiplier.

Example: Show me a startup in the YC job board based in Canada (there are many these days) that is hiring locally only for software engineers.