Yes, you can critically hit with ray attacks (and anything involving an attack roll)
Using Channel Ray means your Channel Energy ability is a ray effect rather than a burst:
When you channel energy, you can project a ray from your holy symbol instead of creating a burst.
And you can critically hit with ray effects, as per the general rules about magical effect targeting:
If a ray spell deals damage, you can score a critical hit just as if it were a weapon. A ray spell threatens a critical hit on a natural roll of 20 and deals double damage on a successful critical hit.
The verbiage in this section does often refer to spells, but the rules are valid for any ray effects regardless of whether it's produced by a spell or other ability. Ray effects are generally treated as a kind of weapon for most purposes by the rules - including the option to take feats like Weapon Focus (Ray) and Improved Critical (Ray).
It's also explicitly confirmed that you can critically hit with close range touch effects:
A touch spell threatens a critical hit on a natural roll of 20 and deals double damage on a successful critical hit.
And of course this is all in keeping with the general rule about critical hits:
When you make an attack roll and get a natural 20 (the d20 shows 20), you hit regardless of your target’s Armor Class, and you have scored a “threat,” meaning the hit might be a critical hit (or “crit”).
A spell that requires an attack roll can score a critical hit. A spell attack that requires no attack roll cannot score a critical hit. If a spell causes ability damage or drain (see Special Abilities), the damage or drain is doubled on a critical hit.
If you're making an attack roll in order to hit the target, you have the potential to critically hit. However, this is only relevant if your effect does hit point or ability damage/drain; otherwise, a critical hit produces no extra special effect.