Never ever ever EVER ever lie to or mislead CBP/CBSA.
Be completely honest.
"I am taking these flights to earn miles to reach a higher status on Air Canada. I will be in the country approximately forty minutes."
When I did EYW and crossed a bunch of times in one day, I just said "I'm participating in an Air Canada contest to earn miles." That resulted in "Okay have a nice day." from both CBP and CBSA.