As long as it doesnt have any nicotine (which, of course, flavors dont) there shouldn't be an issue with importing into Canada. Any duty, etc., will depend on the dollar value and how it's shipped. If shipped through UPS or Fedex, they tend to want to add on a really high (around US$50) brokerage fee on top of the customs/duty fees. If shipped through the post, then it depends on the dollar amount that's declared on the customs form, if it slips through unnoticed or not (for higher value shipments), if it's marked as gift, etc. If it's declared as being CAN$20 or less, then there's no duty/taxes. If it's got a higher declared value, then there's duty/taxes and CanadaPost can charge a CAN$9.95 brokerage fee.
That being said, if they should decide that it's a tobacco product (even though it's flavorings) then the CAN$20 limit doesn't apply and there's taxes/duty on it even if it's CAN$10 value.
A handy calculator for estimating the duty/taxes for shipments to Canada
https://www.crossbordershopping.ca/calculators/canadian-duty-calculator
All of the above is from info gleaned from posts on various forums, incl. ebay's, and is not from my first-hand experience (since I have never lived in Canada), so it may or may not be 100% correct.
Edit to add - any taxes, etc will be paid to the courier (CanadaPost, UPS, Fedex, DHL, etc) upon or after delivery
