"Syrphid fly" refers to an entire family of insects, the Syrphidae, which are bee and wasp mimics. They resemble bees or wasps, which confers some of the natural defenses and safety that would be accorded those more dangerous species that they emulate.
Many syrphid flies are nectar and pollen eaters, and so will be attracted to flowers and provide pollination services. Many of these species are not nectar-robbers but pollinators, though we don't necessarily think first of flies when we think of pollinators.
This family is quite large and diverse. I am not, for the most part, able to identify particular species of syrphid fly. Sometimes it is obvious that two individuals belong to different species; other times, it takes close observation.
There were quite a lot of syrphid flies visiting the flowers of the insect gardens in the Montreal Botanical Gardens. They were mostly of the same size and shape, so probably the same genus. It wasn't until later when I was looking at my photographs that I realized that there were multiple species. Take this one here:
Likely these are two different species (I say likely because I am not certain of this; it is theoretically possible that there might be extreme polymorphism in a single species, but unlikely).
As I was looking through the photos another thing jumped out at me. In that first photo, the syrphid has a strange, bulgy yellow protuberance between its eyes. I wondered what it was: mouth parts? A sensory organ of some sort?
So I trotted down to reddit and asked the helpful entomologists on /r/whatsthisbug about it. I was told that that yellow protuberance is actually the antennae, which are frequently heavily modified in syrphid flies. So. Syrphids can have very strange-looking antennae indeed.