True Strike Guiding Strike

[Hilary]

Would the effects of the True Strike Cantrp followed by the War Domain Channel Divinity (effect) Guiding Strike stack? Would both rolls (advantage) be at +10?

[Dork_Forge]

Would the effects of the True Strike Cantrp followed by the War Domain Channel Divinity (effect) Guiding Strike stack? Would both rolls (advantage) be at +10?

Yes they would stack, you don't add the modifier to both rolls, rather you roll two d20s and then add the modifier to the highest of them.

[Chronos]

It's the same as with any other modifier to your attack roll, like your ability score modifier or your proficiency bonus.

Also note that you don't even use the War Cleric ability until after you've rolled the die (or dice, in the case of advantage). If you roll and roll well (likely, if you have advantage), then you can just save the channel divinity for another time.