Mark,
I am a Canadian in Canada and my understanding of RIFs "Retirement Income Fund" is not great but the gist of it is that your registered money goes into it from your RRSPs after your 71st year. Money must be withdrawn (thus subject to taxes annually)

I don't believe there is any restriction on purchasing US stocks. Again, I assume taxes are paid at source but Canadians can apply taxes paid against Canadian requirements. I personally need to learn more of this for my own trading so I will follow up.

Bruce