Walgreens is not in Canada
Walmart only relates to Canada at the present time.
No business wants to lose a "customer", but to do business, it must make business sense - otherwise in the long run it could be detrimental to one's business plans.
Also remember that WC was in paint department of Walmart (not ideal department of that retailer imo for optimal sales); while we did see some photos of it appearing elsewhere, I suspect those were limited stores or during "testing" periods.
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What happens or doesn't happen in Canada (retailers, sectors, etc) may not be indicative of what will happen in USA or another countries. Notice for example we are already in grocery in two countries, but as of yet haven't penetrated Canada yet for that sector.
Just because we landed London Drugs (pharmacy) in Canada, doesn't mean we will land CVS or Walgreens in USA. However having experience in that sector doesn't hurt the odds (for growth in the sector) and experiences/knowledge can be gained and potentially applied to new accounts in the sector.