This is a much more complex question that it would first appear. The problem with answering it is the definition of "Celt", the Celts originate from the Halstatt culture and migrated into Western Europe taking their culture with them. The term Celtic for the Scottish is incorrect as these people were Picts and Scots, the first being indiginous to Scotland and the latter originating from Ireland coming into Scotland via the Western Isles.
A big problem when likening Gaul or Britain to the Germanic and Norse peoples is that the Gauls and Brittons were Romanised 500 years before the Germanics invaded. When the Saxons and Norse reached Britain the Romano-British had been Christianized in 3rd/4th centuries AD, however they then converted to the new Heathen faiths until this was again Christianized during the 8th and 9th Centuries. Before Christenization the Celts of Britain had been Romanized so many imported gods had been included into their belief system or had replaced existing gods.
It was not until the La Tene period that we have evidence of the "humanization" of the Gods and there we start to see similarities, Wotan/Odhinn is often portrayed wearing horns and carrying a sword and spears, the Celts have a horned god in their sculpture.
Primary sources tell of Druids and temples, such priesthoods or offical buildings are not as evident in Germanic beleifs.
The majority of Celts did not have a written language unlike Picts & Irish Celts (Ogham) or the Germanic/Norse Runes so any evidence of religious belief is that which is documented by the Romans or can be excavated in the form of artifacts.
To fully understand any similarities you must ignore all modern reconstruction of these religions (Druidry, Heathenry and Celtic Reconstruction) and look only at the acrhaeological and primary documentary evidence.