For those who are reading this post. We were able to implement the Moneris as a Payment gateway for this customer.
When we first open the Payment Gateway option, select Moneris.
Below is the window that opens up. Now, customer has to enter the StoreID (which is Merchant Number) of their Moneris account and for the API token, they can find that information in their Moneris Merchant account. They can follow this li to find the details. nk
Once they enter the information for the above 2 fields, it loads the page where it says the confirmation (connected successfully).