The father of your ancestor Ephraim Sercombe was John Sercombe, born circa 1793, who was married in 1811 at Clyst St. George, Devon. At the time of his marriage he was of Holcombe Burnell, Devon. I do not yet know his parentage.
Marian's Ontario Sercombes descend from George Sercombe, who was baptized in 1790 at Dunsford, Devon. I know George's ancestry for several generations before this.
Holcombe Burnell and Dunsford are adjacent parishes, so it is quite likely that George and John were related somehow. George did have a brother John, but I don't think he was yours. I am open to being proven wrong on that, however. In fact, looking back at my evidence so far, this question definitely deserves a closer look. If you'd like some suggestions on how to investigate further, please drop me an email.