I was reading this book about early North American exploration. It said
that the a portion of the French priests that came over to convert the
Native Americans did so with the belief that they were the lost tribe of
Israel.

Could have been. The indigenous population of the Americas resulted from a
mixture of people from various parts of the world for many hundreds, if not
thousands,
of years before the Columbian expeditions.

The original missionary priests in the Mississippi vallley reported discovering
native tribes with blue and hazel eyes, and fair skin. In New England, three
British missionaries were about to be burned at the stake. Two were English,
the third had
grown up speaking Welsh as a child. As the Native Americans were geting ready
to
light off the pyres, the Welsh missionary began calling out to God in his
childhood language. Many of the words were so similar to the language used by
the tribe that had captured these missionaries that some of the captors
understood that he was calling out, in a dialect of *their own language* to a
powerful spirit for help. The missionaries were released unharmed, as a result
of this amazing "sign".

There are literally scores of similar accounts, those are the two I remember
most easily.