I am canadian citizen, live 100% of in Canada. Purchased US funds through TFSA and RRSP. Received a Schedule K3 from USA. If fill out a W-8BEN is that all I need to do?

Basically what I am asking is if buy US funds through canadian TFSA and RRSPs accounts, if I make a gain do I need to pay the USA taxes or if I fill out this W-8BEN form can I ignore the USA Schedule K3 documentation?