If you're planning on going and returning in the same day then going to Tofino may be a bit of a push unless you get a motel there for the night and return the next day. Otherwise you won't get to see everything on the way there - Cathedral Grove, Pt. Alberni (a delightful blast from the past reminiscent of the '60's), Long Beach on the west coast of the Island, all the galleries and other things to see in Tofino.
For a single day trip I'd recommend going to Chemainus, a lovely little touristy town to walk through all the shops and view all the murals on the walls. Or go to Coombs, then to Parksville and on up through Qualicum and on to Courtney along the old coast highway. It's a beautiful drive.
Or go to Butchart Gardens - but you will have to leave the dog in the car while you're touring there.
The Butchart Gardens - Home
Which ever place you do go to you should make enquiries first about where you can take your dog and remember your dog will have to remain on a leash in all public places and provincial parks.
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