I emailed E*Trade Canada about buying and selling USD investments inside an RRSP. This was before I knew anything about at all. Eventually I received this reply:

You can only keep Canadian dollar in rrsp account. You can buy US stocks but the money will be converted to CDN dollars. It is not possible to sell US stock and then buy more US stocks without converting to USD to CDN. Etrade is working towards a option so that you do not have to convert funds back and forth in rsp account.

Sounds promising. At least they are looking into it. Although the more I think about it, this forced exchange between USD and CAD currencies is not such a bad thing. As I've said before, my biggest problem before was that I would trade too much. Buying and selling things, reacting to the market. With the 4% exchange hit, it is much less likely that I am going to want to go back to my old active trading ways.