If i'm not mistaken, there is currently no shuttle service from Square One to Canada's Wonderland at this time. It usually runs during when Canada's Wonderland's opening season takes place.
Anyways, If you want to get there, follow these steps (although I used separate trip planners from miWay.ca, Brampton Transit and York Region Transit/VIVA):
1) Take the miWay 19 bus heading north to the Shoppers World Bus Terminal. Ask for a transfer
2) Get off at the Shoppers World Bus Terminal.
3) Transfer to the Brampton Transit bus route #11 heading eastbound. Please give your miWay transfer to the driver and ask for a Brampton Transit transfer. Arrive at Steeles Ave. and Bramalea Road.
4) Get off at that intersection and transfer to the Brampton Transit 15 bus heading north. Get off at Knightsbridge Rd. west of Bramalea Road. Walk to Bramalea Road north of Fleetwood Cres.
5) Take the Brampton Transit bus route 1 heading eastbound. Please show your transfer to the driver of the route 1.
6) Walk to a stop located at Ebenezer Rd. at The Gore Road in Brampton for a transfer.
7) Take the Brampton Transit bus route 50 heading southbound.
8) Get off a Highway 7 and the Gore Road.
9) Transfer to the 501 Züm bus heading east to York University. Ask for another transfer if you can.
10) Get off at Highway 7 and Interchange Way in Vaughan.
11) Take the northbound YRT 20 bus at Highway 7 and Interchange Way. Your Brampton Transit transfer is accepted on that route, but I cannot guarantee if they will accept it.
12) Get off at Jane and Springside Road. The 20 usually goes inside the Wonderland Bus Loop, but only when Wonderland is in session.
From what I had estimated, it will take around 2 hours using this method. You might have to pay different fares for your journey. The miWay fare will be $3.00, while a Brampton Transit fare is $3.00 as well. YRT/VIVA fare is $3.25 (for zone 1). You can also get the GTA weekly pass, but it cost $52CDN per week. If you pay just the exact fare and as long as your Brampton Transit, miWay or YRT/VIVA transfer DOES NOT expire, you'll be fine.
For your reference in regards to Brampton Transit/YRT-VIVA transfers: http://www.yrt.ca/fares/brampton-integration-policy.asp
I hope this helps - unless someone can clarify and reinforce on what I said. Cheers.