Can iTunes cards pay for Apple Care + ?

Apple care + is not included here -> What you can buy with your Apple Gift Card or Apple ID balance

What you can buy with your Apple Gift Card or Apple Account balance – Apple Support (UK)

For sure -> Call Apple Support at 1-800-APLCARE.

iTunes cards (costco has a sale)

Be alert with Apple Gift Card or App Store & iTunes Gift Card on sale.

See also -> About Gift Card Scams -> About Gift Card Scams - Official Apple Support

Buy at an Apple Store or an Apple Authorized Reseller in your region. 

i have bought at costco before and their cards are legit

👍

i had the apple guy tell me that any card in canada goes toward apple balance

That's absolutely true.

See -> Add money to your Apple ID balance

Add money to your Apple ID balance – Apple Support (UK)

• Then use your Apple Account balance to buy apps, games, music, iCloud+ and more. 

i do know that you can't use the card to buy an iphone

Check here -> Shopping Help - Payment & Pricing

Payment, Financing, Refunds and VAT - Shopping Help - Apple

For sure -> Call Apple Support at 1-800-APLCARE.