₪₪₪ Do I have to 1) file a U.S. tax return and 2) pay U.S. taxes for gains from the following activities?

a) shorting stocks listed in U.S. stock exchanges (borrowing the stocks to be sold, and later repurchasing identical stocks for return to the lender)
b) trading stock option, such as buying calls and puts

I am a nonresident alien (Canadian) and filed a W-8BEN. I greatly appreciate your answers. If possible, I would also like to know which documents could point me to the answers.