Arriving from the US, you go directly to Canadian customs, and there is no arrival lounge. You would have access to the domestic lounge prior to your flight to YHZ, but that is post-security, and I don't believe they have any shower facilities.

I'm not sure if any airport hotels have a day rate, but you might consider getting a day pass from the Goodlife Fitness location in terminal 1 just outside of international arrivals. They have shower and change room facilities.

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