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If you go to, say, Guatemala (outside the 90-day clock area) for a short while before returning to the US via Canada, that will restore the clock. However, if you stay for close to 90 days in the US before doing this, then, at the US port of entry, the CBP officer is likely to assume you intend to live in the US by means of visa runs. If they assume this and you're unable to convince them otherwise, you will be refused entry and almost certainly prohibited from entering under the VWP again (meaning you'll have to apply for a visa)