My understanding is that the two markets are supposed to be similar. When a security is cross-listed between two exchanges, a partial market fragmentation can exist. The two prices of these stocks are co-integrated and therfore the pricing differences are usually corrected within a few days. This is the same for stocks which trade concurrently on the NYSE and the TSX. There are always periods which one may seem more advantageous via stock price because of exchange rates, but they generally stay close together.

With that said, the time difference can play a large factor. The Oslo Borse at their close is usually similar to the open of the TSX (e.g. Closed in Oslo @3.20 CAN, opened in Toronto @3.20. )