Yes, you are correct that it is a juvenile Rainbow Trout.
Juvenile Rainbow Trout has a pink stripe along the lateral line. Juvenile Atlantic Salmon does not have a pink stripe along the lateral line.
All juvenile salmon species, regardless of genus Salmo or Oncorhynchus, have parr marks (dusky blue thumbprint-shaped oval blotches on the side of the body).
Juvenile Atlantic Salmon, at least the strains stocked into Ontario streams, also has red spots along the lateral line. Although not always, some red spots are flanked by parr marks on either side. Juvenile Rainbow Trout does not have red spots.
The ventral fins (pelvic and anal) of Rainbow Trout are often (but not necessarily always) pink with a thick white margin. The ventral fins of juvenile Atlantic Salmon is never pink (usually tan, gold or orange) and a thin white to pale margin is present sometimes.
Black spots of juvenile Rainbow Trout are much smaller than the pupil without halos. Black spots of juvenile Atlantic Salmon are slightly smaller in size to the pupil and often with pale halos.
Juvenile Atlantic Salmon