Umm... sorry, no, they are not Canister balls. Note that the original poster says they measure 2.38-inches in diameter. According to the 1861 Ordnance Manual, no Canister balls were that large. However, the Shot Tables in the Manual say that 18-pounder (5.3"-caliber) Grapeshot balls were precisely the size of these two balls.
As a caution-note for inexperienced collectors who may read this post, I feel I MUST mention that similar-sized balls, with a mold-seam, have been manufactured for non-military purposes, even up to today. So, the next test is to weigh these two balls extra-precisely. Balls of this size from the 20th Century tend to be made of steel (not cast-iron, as civil war ones were), and steel is a heavier metal than cast-iron. According to the Shot Tables, 18-pounder caliber Grapeshot balls (all of which were cast-iron) weigh precisely 1.8 pounds (1 pound 12.8 ounces). If these two balls weigh more than that, they are definitely modern-era steel balls.
By the way... the size-&-weight charts in the Ordnance Manual's Shot Tables can be viewed on the Internet, for free, at:
Descriptions of shot for smoothbore guns
Regards,
Pete [P.C. George]