Aside from the very obvious patterns on the body that identifies your fish as a Northern Pike...
Redfin Pickerel (and its subspecies Grass Pickerel) has full scaled gill cover and cheek.
In Northern Pike the cheek is full scaled but only the upper portion of the gill cover is scaled. The lower portion of the gill cover is scaleless.
Redfin Pickerel is only found in the US. We do not have Redfin Pickerel in Ontario. We do have Grass Pickerel in Ontario and I have caught a few in recent years.
Here's a picture of a Grass Pickerel from Ontario. You can see that the gill plate is completely scaled. The pattern may look like a Muskellunge. However, the cheek and gill cover of Muskellunge is scaled only on the upper half. The lower half is scaleless. The presence and absence of scales on the cheek and gill cover is the positive identification characteristics between Grass Pickerel, Northern Pike and Muskellunge.
So far, none of the Grass Pickerel I've caught exceed 8 inches. This is their average adult size, but they can potentially reach 12 inches.
Again, a recap:
Grass Pickerel - cheek (fully scaled), gill cover (fully scaled)
Northern Pike - cheek (fully scaled), gill cover (upper half scaled, lower half scaleless)
Muskellunge - cheek (upper half scaled, lower half scaleless), gill cover (upper half scaled, lower half scaleless)