Grizzly is a Canadian built M4A1 so it has a cast hull and is usually on the Canadian Dry Pin track with the 17 tooth sprocket. However, some Grizzlies have been put onto standard US track, the Grizzlyfly being an example. The other giveaway is they are all fitted with a three piece front yet have a full width M34A1 mantlet. Even this isn't a guarantee as the front can be changed to a single piece.
The Belgium army museums M4A1(76) has a three piece front which is 'wrong' but shows that with shermans, almost anything is possible. Grizzly hulls also have a general steel foundry symbol on the glacis plate, a G in a shield but contrary to what some have written, this does not stand for Grizzly and indeed appears on other tanks and even M26 pershing turrets.
The only way to be sure is to inspect the vehicle as the internal and pioneer tool stowage is different on a Grizzly.