I don't think there's an iPhone (besides the very first one) that won't work in Canada or with Telus. Telus has the 3rd gen SE on their site, as does Apple Canada.
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I'm not sure if it will work with telus prepaid though. For instance, Volte isn't available to people who are using prepaid, and people who use prepaid don't experience an increase in speed from 5g networks.