Hi Jonathan, 
Here is the address to send the cheque: 
RBC Dominion Securities 
#1100-1708 Dolphin Avenue 
Kelowna, BC V1Y 9S4 
Just so you know our firm charges a administration/trustee fee for Registered accounts each year as do all full service brokerage firms (Nesbitt/Wood Gundy etc).  It is for the work involved in reporting the accounts to Revenue Canada.  For accounts holding only bonds, mutual funds and trust units the fee is $45 dollars plus taxes.  For accounts such as yours holding the above plus stock positions the fee is $125 dollars plus taxes each year.
We can rebalance your account to take positions in only mutual funds and trust units but you are not allowed to add any money to the account to buy new positions.  
Only Credit Unions and Banks provide fee free RSP accounts and those usually do not include stock positions.  I guess it is your decision on how you would like to proceed with this account.  If you want to check other firms to see if they would hold the RSP account for no fee you can certainly do that but if you decide to stay with RBC Dominion Securities they will charge you each year.  Sorry for the bad news.  Of course if your account goes up even 5% per year you would have a gain of $2500 dollars and a $125 dollar fee would be a small part of that gain.  We could sell $600 dollars worth of something in the account to generate cash for the fees for 4 years if you would like, That would get you some time to see if you remain in the US.
Let me know how you would like to proceed. 
Dale Onrait, BSP MBA 
RBC Investments-Kelowna 
1-800-756-2211 or (250) 712-2191