[MENTION=432748]mixedpuppy[/MENTION]
Really appreciate your reply and calculation about the input/output.
My cards are CSR and SPG. I basically use CSR for travel related things (e.g. air tickets, car rental, and hotels), where it gives me three points a dollar. I think it should give 5% benefit at least. Even considered exchange loss, it should be at least 3%. I can easily spend way more than $5000 (break even point), so I think it is worthy to use it here.
In terms of SPG, my plan is to get the open account bonus ($5000 for 35k points), which is a no-brain worthy for now. Given the merge between Marriot and SPG, let's wait and see what will happen to SPG next year.
Last reason I use US card is I think CAD is under-valued now and I am expecting to get 0.9 exchange rate at least for CAD:USD in two or three years. (cc [MENTION=724557]Sintaku[/MENTION] )

[MENTION=227449]garykung[/MENTION]
I also think that is all I can do. It means no more new cards these few years tho.