Create a group based on the sales rep in the Crystal Report, and place the:
...in the footer of the group.
that, unfortunately gives me the sum for all the sales reps
Then you aren't grouping by sales rep, or the sales rep info isn't what you think it is.
When I look at the Group Expert I see the field SalesRep in the "Group By" portion. Then, using the formulas I've got listed above, I add the formula from your answer in the GroupFooterSection1 area, it then displays the total SUM for all Canadian Commissions, not the individual rep.
So on the report, you see a group header above the details section, and the corresponding group footer underneath - the formula is in the group footer section...
Is any other data relating to sales rep coming out properly in the grouping?