I want to write covered calls on a stock that is listed on both the TSX and NYSE. I would write the US listed calls (tighter spreads and better value) but buy the stock on the TSX because my account is with IB, my cash is in CAD, and I would pay margin interest if I purchased it on the NYSE/US side. Question: If the calls get exercised, exactly what happens? Would the TSX purchased stock be sold (removed from my account) as usual and the USD proceeds credited in the USD side? Or would I have to buy it on the US side (which would seem an odd thing to have to do since the common stock is the same regardless of which exchange it's traded on). I'm accustomed to writing puts and call (naked and covered) on both US stocks and Canadian stocks (options traded on the montreal exchange), but I've never done it the way above. Anyone?