Canadian university grad looking to pursue his MBA

I've been a lurker here for awhile and the advice here has been incredibly valuable. I'll be graduating in the fall and will be starting at a Big 4 firm in Toronto.

My main reason for being here - I would like to pursue an MBA in finance at a US school. My GPA is not strong (will most likely graduate somewhere in the 3.4-3.5 range depending how the rest of this semester goes.

My plan is to stay at Big 4 audit for 2-3 years (until I get my CA), go for an MBA in finance, and then look towards a Big 4 advisory position, or at a consulting firm.

I know I will have to do exceptionally well on the GMAT. I was wondering what else I could do to be a stronger candidate. Any organizations I should get involved in? Volunteer experience?

Thanks.