Channeling Spells thru your Weapon and Critical Hits

[Curmudgeon]

1. Does the weapon crit range extend to the spell being channeled?
2. Does the spell now crit whenever the weapon crits?
3. Does the spell share the crit multiplier of the weapon as opposed to normal, simple doubling?

1. No. Weaponlike spells always threaten on a natural 20. (You can expand that with Improved Critical for the type of spell you're using; see Complete Arcane on pages 72-73.) The fact that you're delivering two effects with a single attack doesn't change the separate rules associated with those attacks.
2. No; see above. If it's a weaponlike spell it's got its own threat range and will need its own critical hit confirmation roll.
3. Again, no. If it's a weaponlike spell it follows the rules for such. If it's not weaponlike it's just along for the ride and won't ever be multiplied regardless of what rolls you make for the weapon attack.