Would I need an ESTA to get back into the US from Canada with a Swiss?
You need a valid ESTA to enter the US using the Visa Waiver Program regardless of the means of travel to the U.S. Additionally, if you entered Canada from the U.S. and your prior entry was under the VWP, you do not get a new 90 day period of authorized stay, only the balance of the 90 days from your prior entry. In any other circumstance you will need a valid visa to enter the U.S.