1820 North West Company Token

Looks copper, from the photos. I assume it was a ground find at some stage (metal detector, gardening, etc). In that sense, the token has already been "cleaned" ie removed the dirt etc from it.

Once a coin is in a corroded state like that, there's very little that can be done to improve it, and just about anything you might do to it (eg. acids, ammonia, electrolysis, harsh scrubbing) will only make it look worse.

The pale white flecks on the obverse ("heads" side) are worrying me; they might be the start of bronze disease. Keep an eye on it, and if it appears to be spreading over time, it may need treatment. Otherwise, I'd recommend leaving it as it is.