Guarin comes from the Germanic personal name (from Frankish and Lombardic tradition)
*Warino, from
warin, "to defend, to protect" (derivated from
war, "guard"). The Low Latin form
Guarinus is attested at Italy in 7th century in the forms
Varinus and
Guarinus (De Felice, 1980).
It was popular because of saint Guarino de Bologna, bishop of Palestrine and cardinal in the 12th century (name day: February 6th).
Lumia
http://onomastica.mailcatala.com