回複：加拿大短登回美曆險記

I think:
(1) At first, you'd better not say you went touring Toronto. Just saying you are landed in Canada as too many Chinese landed at Rainbow bridge, the office knows it very well.
(2) You'd better say you will use Canadian PR as backup of US GC as US GC takes too long.
(3) You should mention US GC has higher priority, you will give up your Canadian PR as soons as your US GC is approved. If needed, you should say I can give up my Canadian PR now, but unfortunately they can't cancel your Canadian PR as it's Canaian office's business.