Punki,

As Star Gold you automatically get Maple Leaf lounge access and they should offer early boarding. That is it.

Also, they are telling you a fib when they told you that you get your PremEx 100% bonus. Nope. Just flight miles that count as status. Also they don't count for the 10,000 required to earn a book of upgrade certs.

All in all, I would change to AC from YYZ to ORD, UA ORD-SEA. Also, AC probably would not ask for your UA upgrade certs and they issue your UA boarding pass. Just a thought.