You'd have to pay taxes on your US investments either way. Plus you'd be paying taxes to Canada first and then get a credit for that on your US taxes:
"In the U.S., your quarterly dividend income is taxable on your U.S. tax return. Your Canadian tax already paid is eligible as a foreign tax credit on filing to help avoid double taxation."
https://www.moneysense.ca/save/taxes/owning-canadian-stocks-as-a-u-s-resident/
While you missed the boom, there is still growth potential there as they expand into the US as more states allow Medicinal and recreational.
Honestly you've probably already missed the Green wave in the US, unless you wait for a state that hasn't legalized to do so and jump in on a local investment. Colorado and CA already have there networks setup, the biggest issue is handling money. Though we're seeing more Credit unions allow Weed money with stricter rules, which is better than no federal money institution would touch you because Pot.
If you want to go that route, you could invest in POT in a round a bout way by investing in the credit unions that are doing business with the Pot companies and handling their finances.