The downside is, if a merchant signs up with AMEX ExpressWay just to support Apple Pay, that means Apple Pay is costing the merchant extra at this point.I think that American Express, Moneris and Global Solutions have their reps calling merchants, encouraging them to turn on ExpressWay which enables ApplePay to work.
For example, if you paid for gas or food with a regular Visa chip card, the merchant would only pay a 1.5% - 2% fee. By using your AMEX card, a retail merchant has to pay a 2.9% fee + 0.15 per transaction, and a restaurant or hotel has to pay 3.5% + 0.05 per. (Which is why many places don't take AMEX, especially if they're already operating on a slim margin.)
The upside is that this extra cost could cause merchants to join the push for other cards to support Apple Pay in Canada.