A while back BMO Investorline informed their RRSP customers that they will be permitted to hold U.S. dollars in their RRSP accounts. This has the potential to reduce the number of costly currency conversions between Canadian and U.S. dollars. However, investors still need to take action to avoid automatic currency conversions on dividends.
Like cash accounts, RRSPs now have a Canadian side and a U.S. side. However, you can still hold U.S. securities on the Canadian side. In fact, keeping everything on the Canadian side of accounts is the initial default. This means that when these holdings pay a dividend in U.S. dollars, the dividend will be automatically converted to Canadian dollars (with the implicit conversion charge).
No doubt many customers will prefer to have only Canadian dollars. For this reason, I can see why BMO should not automatically move securities to the U.S. side of RRSP accounts. On the other hand, BMO will continue to collect fat currency-conversion fees from unwary customers.
If you prefer to hold dividends in U.S. dollars and not pay for the currency conversions, you have to call up a BMO Investorline representative to have U.S. securities moved to the U.S. side of your account. I haven't found a way to do this online.