Minecraft's latest snapshot added entity scale as an attribute, so I had to play around with making some giant (and tiny) wolves.

Instructions:
In Minecraft Java and Bedrock the attribute feature was added. So you can look at an entity and run the attribute command:
/attribute <uuid> Minecraft:generic.scale set base <N>

The uuid is the entity’s ID value and you get by using the TAB key on PC after entering attribute.
N is the base size, which is variable from, 0.0625 (1/16) normal size to 16 times normal size.

Alternatively if you just want to make all the wolves huge you could use his variation:
/attribute @e[type=minecraft:wolf] minecraft:generic.scale set base 16