Impala, Chargers, and Tauruses are usually Premium (PCARs) in Canada. Fullsize is usually a Camry, Fusion, Chrysler 200, Malibu Limited, Altima, or Sonata.

What car is in stock really depends on the agency. Hertz leans toward Toyotas, Hyundais, and Fiat Chrysler vehicles. National/Enterprise/Alamo has the widest range skewing towards Altimas, Sonatas, Fusions, and Malibu Limiteds. I don't rent enough from Avis Budget in Canada, but I've heard that they have mostly GM, Ford, and FCA vehicles.

There isn't much difference between standard and fullsize cars nowadays. The pricing is often the exact same. Standard cars might be slightly smaller (like a Chrysler 200) or have a cheaper retail price.