I have an celeron that bottleneck my gpu and i need to know if i3 is good for gaming im not targeting for ultra or high settings and my mother board support only 7 th gen max cpus and i dont have money for an i5 7100 or 6400
Not really, its a dual core, which struggle in modern games. Bare minimum you should aim for a i5 and only if you can get a good deal on one used.
You may want to consider saving your money and updating your system to a Ryzen platform, you can get the Ryzen 1600 AF (essentially a 12nm 2600) which is 6 core 12 thread for 85 USD, a cheap B450 for around 50 USD and 8GB of dual channel RAM which is about 60 USD
It depends on what games you play. Most games should run fine as in you should be able to play them in High-Ultra in 1080P, only a small percentage of games that require a lot of CPU processing such assassin Creed Odessy, Total War: Warhammer, Stellaris, Final Fantasy XV would cause bottlenecking issues however in the future games will certainly require better CPUs thus you would need to upgrade your CPU again in 2-5 years time to still be able to play games at High-Ultra Settings infact most triple AAA games coming out this year/last year prob won't run fine at Ultra Settings (Red Dead Redemption 2 & Metro Exodus).
tldr: Probably a huge improvement over your existing Celeron CPU and should fulfill your needs unless you want ultra settings on every single game at 1080p, it should run most triple AAA games on ultra on 1080p anyways.
I have an celeron that bottleneck my gpu and i need to know if i3 is good for gaming im not targeting for ultra or high settings and my mother board support only 7 th gen max cpus and i dont have money for an i5 7100 or 6400
What makes me a bit puzzled is that you have a GTX 1070, which makes the computer very unbalanced.
I'd rather expect a GT 1050 to go with a Celeron...
A Core i3 will be a notable upgrade but still not enough to reach the level of your video card. I concur with the recommendations from previous posters.