I'm travelling from Orlando to Calgary. Will I go through customs in DEN or HOU?

I'm travelling from Orlando to Calgary. I can either have a flight that has a 56 minute layover in Denver or one that has a 46 minute layover in Houston. Does anyone know if I go through customs at the layover or when I get to Calgary? And if I will even have enough time to go through customs. I'm gone... show more I'm travelling from Orlando to Calgary. I can either have a flight that has a 56 minute layover in Denver or one that has a 46 minute layover in Houston. Does anyone know if I go through customs at the layover or when I get to Calgary? And if I will even have enough time to go through customs. I'm gone through customs to enter Canada before but I would usually have a layover in Toronto. Does anyone know? Thanks.
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