When I open up a regular checking account, I get an ATM/DEBIT card? So what exactly are the pros/cons of using a Visa/MC Debit card over the debit card provided by my bank?
ATM and Debit are not the same thing. ATM is a card that can only be used to withdraw money from the ATMs that belong to that bank (or participate in the same network). In some countries, ATM cards can be used for shopping if the merchant is equipped with an appropriate reader and is participating in an appropriate network.
Debit card can be used for purchases in any store showing the appropriate (Visa/MC) logo, and withdraw money at any ATM showing the appropriate (Visa/MC or the ATM network that appears on the card) logo.
In Canada, there are many stores that take debit (Interac) but don't take Visa or MasterCard. For example, a corner store. In the US the reverse is often true: every tiny place seems to take Visa or MasterCard, but not debit.
A Visa debit card looks like a Visa card to the merchant. It therefore has the benefit of being usable at places that only take Visa. (Substitute MasterCard as necessary.) This benefit is very small in Canada, less so elsewhere. Meanwhile the money is actually coming out of your bank account just like a debit card, which therefore has the benefit that you're not borrowing money, can't accidentally overspend, and run no risk of incurring interest charges. It is also a way to get what appears to be a credit card when you can't qualify for credit.
If you do the majority of your spending in Canada, you don't need a Visa or MasterCard debit card. Your regular debit card (Interac) will work fine for you. If you have a credit card anyway (from another bank or whatever) then again, you don't need a debit card that can pretend to be a credit card.
Visa and Mastercard offer a variety of benefits to their cardholders. It's all in the initial information that may come in one, two or more parcels describing the relationship the two of you are in.
I can't enumerate the services, but it ranges from things like automatic rental car insurance to price matching.
You'll really have to compare the product with your banks'.