CP Multiplier When Evolve

Sorry but this is not how it works.
The CP value is calculated using three things:
1) base values of the Pokémon species (Attack, Defense, Stamina)
2) IV of your Pokémon
3) level of your Pokémon (CP multiplier)
When your Pokémon evolves, only the base values of the species change.
Here you can read how the CP value is calculated http://pokemongo.gamepress.gg/pokemon-stats-advanced
There is no such 2x or 3x CP multiplier, sorry.
But it's true that Vaporeon has a higher Max CP value than the other 2 evolutions. You can observe big jumps in the CP value when the unevolved Pokémon is really weak compared to its evolved form (for example Magikarp -> Gyarados) but that is kind of pointless.

CP is an aggregate number (so in that regard akin to "stat total" or "base stat total" when discussed in contexts outside of the game), as it cryptically summarizes the attack, defense, and stamina/HP stats.

Evolution in this game is like evolution in the main games: your pokemon's level remains the same, only, in the case of this game, we're not clearly told our pokemon's level.

Now, in the main games, all the Eeveelutions are designed to have the same base state total, 525. They can have different stat totals when they have different IV's and especially when their nature exaggerate their different stats differently (i.e., a +Speed nature Jolteon gains a lot of speed while a -Attack nature Flareon loses a lot of attack), but usually they'll have similar stat totals (similar stat total aggregate numbers).

The base stats in Pokemon Go, however, are not designed with such initial parity in mind (this is absolutely evident comparing the stats of Jolteon and Flareon), but really are not individually designed at all, instead simply filtering the stats of the Pokemon in the main games through a common formula. The common opinion is that Vaporeon "wins" in this regard relative to its brethren, due to the mathematical grouping of its stats in the main game. (People might also see it to be tankier in battle--in true terms it's losing more HP on the same moves with the same reception than the other Eeveelutions, only it has a lot more HP, and people are going by the graphic sum of its health.)

Yes, evolving an Eevee into a Vaporeon will result in it having a higher CP than if you evolve it into a Flareon or Jolteon.

CP is slightly misleading though, as you're told your pokemon's HP and not told in-game just what CP truly represents--HP is basically "double-counted", or slightly redundant. (It'd be like being told your pokemon's HP stat in the main games but not its attack, defense, special attack and defense, and speed, but being told its "stat total" instead.) Flareon and Jolteon actually both have higher attack and defense, but Vaporeon is the beneficiary of the CP formula.

That's not to say CP is often a useless aggregate, as, while this site breaks down "dps", or damage per second, CP is a very good rough estimator of damage prior to consideration of moves, or "base damage potential times potential number of seconds in battle".