Basically, major difference is mobility patterns (while nodes in wsn may be static, nodes in vanet are always mobile) and major similarity is communication channel - wireless.

This might also help: http://www.ens-lyon.fr/LIP/pe-wasun10/Barba.pdf

Please read the article below:

Karn, Chaitanya, Gupta, C.P.,” A Survey on VANETs Security Attacks and Sybil Attack Detection”, International Journal of Sensors, Wireless Communications and Control, 2015, Vol. 5 (2),1-18

similarity:  they are infrastructure less if not centralized, they use wireless medium

dissimilarity: wsn has no mobility (static) and vanet has mobility, wsn is deployment is random or organized in an area but vanet is restricted in an area (roads), wsn uses 2.4 ghz n vanet use 5.9 ghz(ieee 802.11p), vanet is used for road safety (accident ahead broadcasting) and comfort applications (media downloading) etc and wsn is used for many types of applications like military, agriculture, defence, road safety, medical, iot, intelligent transportation, etc. , vanet is restricted to limited applications on roads but wsn can b used in many applications, etc.