Why do you think Mack is so hooked onto that Bauer hat? It’s all he has been wearing and he is known to switch around hats a lot.
Okay, for me there’s three options, so let’s see. First option is, it’s Will’s hat, he has many of them and he thought letting Mack have one was cool, like sharing is caring sort of thing. So he gave Mack one and Mack holds it precious and uses constantly because well, it’s Will’s. We have seen the warrior’s hoodie Will had one time which I’m sure Mack gave to him, so I wouldn’t be surprised at all if they gift each other those sort of things. Just like Mack’s Canada stick in Will’s house, surely Mack gave him that.
Second option, it’s also Will’s BUT Mack stole it somehow. He maybe found it one day at Will’s place and just took it. Said “Oh I like this, surely Will won’t mind” turns out Will didn’t even notice it was gone until Mack texted him a tentative “hey I grabbed your hat by accident” which was a lie but it made Mack feel slightly better about having stolen it. Will just let Mack keep it.
Third option. The less funny one. It’s team Canada merch, they were sponsored by bauer (i think) so it would make sense for Mack to have it, sorta. We have seen Mack not sticking to one brand, like with his sony headphones (found using airpods) or with mercedes (he drives an audi i think) so yeah, he might be betraying his CCMness but Mack doesn’t really care. Besides, like I said it’s his team’s merch.