I think more and more we will see or hear of SAs being upfront with clients on prespend.
If I were you I would sign up for one of those online services that provide notifications when bags drop and get a mini Lindy online on H Canada. It will take a while because they don’t appear as often, but at least it won’t use any of your prespend. Check with your friends that shop at H there if they know. In Europe they don’t care, but apparently in the U.S. some managers check the bags you’ve been buying online.
As for the Constance, I don’t know how is resale in Canada, but in the U.S. I only buy bags that are not B or K on resale, H online or H abroad. Resellers in the U.S. are selling new Constance these days close to retail. If you are close to the border, you can always go to a hotel and have a U.S. reputable reseller ship it to a U.S. address there. I heard at CDG in Paris that the prespend in the store was 6.000 euros.
You might want to only buy in the boutique, so I would try to do combination of boutique for Constance and online for ML. If you do that, I think it would be best to get whatever quota you aim for for B or K (1 or 2), and then ask for the other bags towards the end of the year and try to get one or both before the year is over.