I'm married to a Toews and I can confirm that most of the country just sees 'toes'. Except Quebec where she is a 'taos', which is pronounced like cows.
Toews is a Mennonite last name. In the German dialect that the Mennonites speak, the oe vowel combo is very common and makes a long a sound. Another typical Mennonite last name with the same combo and sound is Froese (pronounced like fraze).
The w->v thing is common to pretty much all Germanic languages.