The gardens themselves are impressive and I would expect birds and butterflies to be there however because it can be filled with people, the birds will probably be on the fringes high in the canopy. The Butchart Gardens is a located in the middle of a Douglas Fir Forest so I expect you would mainly find forest species around here.
Now, there are some good birding spots close by to Butchart Gardens that may offer a wider variety of species.
Gore Nature Parkhttp://crdcommunitygreenmap.ca/location ... ature-park
"In April, it would be full of wildflowers and is impressive on its own!"
Oak Haven Parkhttp://crdcommunitygreenmap.ca/location/oak-haven-park