In general cut west from Barrie and pick up Beaver Valley RD down - then down any of the paved NS roads to the Forks of the Credit area.
Amble west on any of the sideroads and then cut south to SR 5 which meanders along until you hit Campbellville road - take that under the 401 and either head west on it over to Twiss area and south on Cedar Springs or go left just after the 401 underpass and swing down Appleby - test your skills on the hairpin at Rattlesnake.
Continue South to SR4 - lovely little road goes west then left at the end down to SR 1
take SR1 across Guelph Line and up the escarpment ( careful of a really sharp left at the top ).
Meander along that to the back of Waterdown and get on to Snake Road.
Take first right on Snake and go all the way across to Ancaster - yes Virginia you may get lost but it's a nice area to get lost in.
Good coffee at Coffee Culture on the main drag.
Get across Hamilton to Ridge Road and follow the top of the escarpment for a while then dip down to HWY 8 and you can take that all the way through then to Niagara on the Lake and pick up the Niagara Parkway.
Can give you a different loop coming home by way of Fort Erie, Port Colborne to Selkirk ( don't miss the slow cruise along Lake Erie ) and then to Dover.
Come back via 6 and you can retrace the back roads or slab it or you can head further west to Long Point but cut down towards the lake ( suggest mapping it ) as there are some nice roads to the south of 3.
My problem is I've been riding the area all my life and can't tell you the name of the roads in some cases.
You could continue 6 north of the 403 up through Guelph and catch the Motocross place at Chatsworth for a break.
http://www.motoparkracing.com/about-motopark.html
There is also York Soaring just 10 min east of Arthur where HWY 9 intersects - good fun if it's a nice day
http://www.yorksoaring.com/