Welcome to the board!
Native plants are generally a good bet as they provide either food sources or other materials that songbirds will be adapted for. There are native plant sales in the spring that are worth going to (e.g., North American Native Plant Society sale in Markham). There are also nurseries that supply native plants. Some will just show up in your garden (e.g., milkweed).
Songbirds will benefit from sheltering trees or shrubs. This will help them avoid predators and they are more likely to hang around your backyard if they have shelter. Anything with relatively dense foliage and/or branches is good.
Fruiting plants, especially those with berries are popular with some songbirds such as robins and waxwings. Sumac, serviceberries, wild cherries, elderberries are all good. Plants that produce seedheads are popular with goldfinches and other seed eating birds. Coneflowers and native sunflowers are good examples. Jewelweed is good for hummingbirds. Anything that attracts insects (most flowering plants) will also attract birds feeding on the insects.
