I picked Questrade specifically because they cater to folks in both the US and Canada. When I asked about cash transfers (USD->CAD and back), they said I'd just need to submit a request, and they'd exchange the funds at spot. :)
One other path, though, is to just buy/sell crypto... Personally, I'm not a fan of any cryptocurrencies, but that's the one aspect where they're objectively better and faster than all the traditional financial methods. (There is no guarantee, however, that the crypto's price won't fall just before you sell it. Might be risky.)