Hi, please be gentle with this Hertz Rookie.

I will be in NYC december and am planning on renting a car for 4 days to drive up state to BUF/Niagara and then head over the border to YYZ and stay for a few nights, before heading back to NYC.

Are there any penalties or other rules I should be aware of for taking the vehicle across the Canadian border?

As BMI Gold I was given Hertz Gold Double Upgrade Vouchers and a CDP code.
Lets say want a prestige Mercedes SUV. Do I book a lower class car and then show the Voucher to get an upgrade? Or is the upgrade automatically processed when I book using the CDP code?

Many thanks for any advice.

Petrus