Depends if it is dry or weathered wicker or whether it has previously been varnished, previousy varnished should be redone the same as it will be sealed and all you are doing is re applying the sealant, better using spirit based.
dry or weathered wicker needs resealed and can take water based varnish, paint or preservative.
I have just gutted some of mine, finely sprayed them with spirit based varnish and relined them
Beware of woodworm they love wicker baskets:'(