Toronto Beaches garden
Volunteer sproted in container this spring
Sun, fairly dry
Fast-growing, twining form
Now 6 feet high from base in green pot
This ‘volunteer’ appears to be from the Celastrus genus, a variety of species of shrubs and vines commonly known as “bittersweet.” It will be easier to get a more definitive identification when this plant flowers, but I will suggest two likely options here. The first is Celastrus orbiculatus, a woody, creeping vine that is classified as an invasive plant in Ontario and should be removed. If it is indeed this plant you will see a white pollen on the stamens. The berries have a yellow capsule that eventually splits to reveal a red, inner seed. The berries appear all along the stems
A second option is Celastrus scandens, a woody vine native to Ontario. It has yellow pollen on the stamens and produces orange capsules that split to reveal orange berries in clusters at the stem tips.
This article from the United States Geological Survey describes characteristics of each type of bittersweet in greater detail and may be helpful in confirming the identification for you American and Oriental Bittersweet ID.