Is feasible to visit Old Montreal or Downtown during a 12-hour layover?

score:8

Yup, with 12 hours it's very feasible and I would definitely go for it. In order:

Yes, there is a "cloakroom" outside arrivals, rates $2-6/day depending on bag size. However, why not just check in your bags for your next flight immediately, and only then set off to explore?
The easy public transport option is the direct 747 bus, $9 return including unlimited public transport in Montreal for the day, travel time 45 minutes plus depending on traffic. If you're really pinching pennies you can take bus 204 to the nearest Metro station and connect ($3/one-way), but this is more hassle than it's worth.
Customs/Immigration time varies wildly, but if it takes over an hour you're having a really bad day. Flights from Mexico may get some extra attention though.
If you already have checked in before you left the airport, an hour should suffice. Otherwise you might want to allow two hours. (Official recommendation is three hours, but this is a bit silly.)

lambshaanxy 99250

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