Here is some info I found. Not sure how accurate it is though! Can anyone out there verify this???
County market - Doubles up to 50¢; no limit.
Cub Foods- does accept expireds - most stores go up to 3 months. A very few are up to 6 months, and a few are no expireds at all - it's up to local management, so it's best to call or stop at the CS desk before shopping.
Econofoods Mart - occassionally doubles up to/including $1 and triples up to/including 50¢. No limites, but only non-expired coupons are accepted.
Evans Supermarket - doubles up to 50¢; no limit.
Rainbow Foods - No longer doubles or accepts expireds.
Sunmart - Doubles up to 50¢; 55¢ and up are raised to $1.00. Occasionally triples up to 50¢ and doubles to 75; no limits.
SuperValue - everyday doubles in some stores. Amounts and policies vary by store - call before you make any plans.