I wouldn't say he is giant size. Define "giant"
Bacca at 12.5 weeks was 8.6 lbs
At 15.5 weeks was 11 lbs
At 9.5 months he was 23 lbs and had pretty much hit his adult size of 17 inches.
At 2.5 years, he is now 30 lbs and still about 17 inches. He is certainly oversize for a Sheltie standard, but I would not say giant. Nor fat. Bacca's extra weight comes from a long and lean body with lots of muscle (as opposed to my Indy who IS fat. Same weight, same height, but short body)
I think at 19 weeks, it's pretty sure that he will grow more, and clearly indicates, at least to me that he will probably end up about the same as Bacca.
I think the pattern is pretty much set at for Miko by now.
But it's just more to love!