But wouldn't that other airline that already uses the maple leaf as its logo be Westjet's main competitor on those overseas markets?

Why focus branding on "being Canadian" when your biggest competitor is also Canadian? I'm struggling to understand how that lifts WS's brand or revenue against their main competitor.

At best, it sounds like they're using this new brand identity to say "hey, we're also a Canadian airline". Not exactly the most compelling value prop...