Yep, There's a ton of content out there on this process. And quite a few threads here from May-June.
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Segment out Canadian leads
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determine who has implicit/explicit consent
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ask list to opt in
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if they don't, set to unsubscribed
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make sure there's a way to log the date and IP of the change (Marketo does do this, but you may want something clearer in the system).
Since this is after July 1, I think you need to opt out all your non permissioned Canadian leads at this stage.