The first thing you want to do is to find the magnetic declination for your maps. Look for a diagram something like this, somewhere in the white border on your topographical maps:
This particular diagram is showing a WEST or NEGATIVE declination. You can forget those terms now - I only chose this image because the declination for Parry Sound is also WEST/NEGATIVE, so they'll look kinda the same.
On your maps it will give you some value like "14 degrees West, annual change decreasing 1.5 degrees". Ignore these numbers on your maps, unless they're very recent - like within the past 2 years or so. Which they never are.
We will get the current declination for our location (Parry Sound) using the interwebs. Simply type "parry sound declination" into any search engine and you will get the current declination for your location, like this:
The declination you will use for Wilderness Traverse 2022 is 10.34 degrees West. Sweet! Now you have to adjust ALL your compasses to correct for that. Here's how.
If you don't adjust your compass, then this is what following a bearing would look like:
Notice that the Direction of Travel Arrow and the Orienting Arrow are pointing in the same direction. You don't want that for WT 2022 in Parry Sound, because you'll be going 10 degrees West of the direction you think you're going. All the time. This will get you lost. Fortunately, most compasses have a handy rotating ring that you can use to cancel out the local declination by moving the Orienting Arrow left or right relative to the Direction of Travel Arrow. In your case, you want to add just over 10 degrees to cancel out the negative 10 degrees of West declination.
Here's how to check if you've done it correctly. Your compass should look something like this:
Notice that your orienting arrow is pointing West (left) of North. In this case they have it at 20 degrees, but you will have it at 10 degrees, so your orienting arrow will be pointing to 350 degrees. Now, place your compass next to the declination diagram on your map (Fig. 1). If you line up the direction of travel arrow with True North, your orienting arrow should be pointing in the same direction as Magnetic North. Congratulations: you're good to go.
If you've corrected in the wrong direction then the orienting arrow will be pointing at around 10 degrees. East (right) of North. Meaning all your bearings will now be off by 20 degrees. Turn it back to 0 and then go 10 degrees in the other direction.
Your compass now works perfectly for this race. Any mistakes you make are therefore on you. No pressure. ;)