Wa Alaaykum As'salaam
I will try my best to reply
1. Has Allah chosen who we marry? (I know Allah knows who we will marry and if we will marry but if we do marry is that allah's choice)
It is ofcourse what Allaah wills that matters, he has already told us for who and what type of individual one should look for as a their spouse.. So it is someone who practices their faith and fears Allaah etc many things that one should look for and be aware of the things that one should stay away from..
However, every individual has their own requirements i guess..
If we arent aware if the person we are about to marry is right or not then we ask Allaah for guidance through Ishtikharah salaah..
2. Is there anyway we can speed up the process of marriage or is the time we marry also predetermined?
Hmm, asking your parents to help you to find a spouse, your sisters, friends. i think i'll let others reply to this question..Im sure there are many married brothers and sisters with experience of this..
3. How do we know If that person is who we marry?
Firstly, you will need to do some research, is this person a God fearing individual, will he/she be able to support me in the times of hardship.. if its a brother, is he able to provide?..if you are interested in them..etc
Like i said everyone has their personal requirements..
I hope someone can reply to you in more depth insha'Allaah
May Allaah SWT grant you a pious husband that will accept you for who you are, grant you happiness in this life and the hereafter Aameen..