If the buyer's cart order does not qualify for any shipping rules you have set up, the cart would show "-error-" for the Shipping amount, and when they try to proceed to checkout, this message would appear: "Please select the Country, enter a valid ZIP/Postal Code, and press the UPDATE CART button." If that is what you were seeing, then the problem was something to do with how you'd set up your shipping rules.
Looking at your current rules, it appears your rules for Canada have some gaps in the price ranges: all of the Max. Item Total figures end in .95, rather than .99 as with your other rules, and since the Min. Item Totals are even dollar amounts, any cart totals in those .96-.99 gaps being shipped to Canada would fail to match a Canadian rule, so they would only qualify for the All Countries rule that covers that price range (e.g., a cart total of 49.97 being shipped to Canada would be charged 23.95 for shipping, rather than 19.95).
We do plan to make shipping rules editable in the new Admin, but I'm not sure if this enhancement will be included in the new Admin as soon as it launches. I gather some new back-end programming is required to make this possible, so if that can't be completed by the time the new Admin is otherwise ready to launch, we may just add that feature a bit later on.