Canada doesn’t have the concept of short term and long term capital gains.
It’s just capital gains, so whether you hold for a year or more is irrelevant. 50% of the gains are tax free and the other 50% is taxed at whatever slab you fall in as ordinary income.
The one key point to note is that as a PR your cost basis in determining the gains is the price of the stock when you moved to Canada and not the price that you bought them at.
As for taxation in the USA, no taxes are due if you’re a non resident (except if you’re a US citizen or GC holder, in which case you also need to report and pay taxes to IRS).