Oh man, I'm just about the last Finn to ask about Finnish music, but even when inspected with my feeble knowledge this list looks very accurate indeed. It doesn't favor any one genre, it takes into account popularity as well as critical acclaim, and you can tell you've given thought to the lower placements too. Must've taken you ages. Nice work, all in all!
Here's a scant few I came up with, who might have a shot:Mikko Alatalo
(the only big name that seems to be missing)Antti Tuisku
(imo deserves it more than Hanna Pakarinen as he is the most successful thing to come from Idols; has had some longevity)Olavi Virta
(this is an interesting one since I'm not 100% clear on your genre restrictions; popularity-wise should be a shoe-in)Petri Nygård
(if only to have another rap act there; not too high a pick obviously, but you can't deny the splash this guy's made; if we we're a monarch, he'd be the king right now)Regina
(this is my personal suggestion to tack on at the very end, maybe replace Haloo! Helsinki, who've had only one hit to my knowledge; it would add more variety as Regina have already achieved some sub-moderate indie faggy acclaim overseas/on Pitchfork and will most likely continue this hot winning streak of theirs by releasing a straight-up moderately received
album this fall
If I come up with anything else, I'll let you know. And again, marvelous list.