Whatever you are most comfortable with. For the most part, stick to your guns.
What openings should I use against when playing a 1700+ rated player?
Whatever you are most comfortable with. For the most part, stick to your guns.
1.e4/ Sicillian/French/London.
Whatever you are most comfortable with. For the most part, stick to your guns.
What is the strongest opening for white and for black???
Whatever you are most comfortable with. For the most part, stick to your guns.

Your question suggests that you are overly concerned about ratings. Whether you are playing a GM or a person who has never played a game of chess in their life, play the opening you feel most comfortable with.
TINSTAABO
"There is no such thing as a 'best opening.' Each player should choose an opening that attracts him. Some players are looking for a gambit as White, others for Black gambits. Many players that are starting out (or have bad memories) want to avoid mainstream systems, others want dynamic openings, and others want calm positional pathways. It’s all about personal taste and personal need.
For example, if you feel you’re poor at tactics you can choose a quiet positional opening (trying to hide from your weakness and just play chess), or seek more dynamic openings that engender lots of tactics and sacrifices (this might lead to more losses but, over time, will improve your tactical skills and make you stronger)." - IM Jeremy Silman (January 28, 2016)
https://www.chess.com/article/view/opening-questions-and-a-dream-mate
The August 2019 issue of Chess lists the top twenty openings compiled from a list of 2507 June games where both players were rated over 2400 Elo. One can not take position on this list too seriously because it is greatly influenced by how the openings are grouped. For example, all the Retis are grouped together, while English is separated into 1...c5, 1...e5, etc. Nevertheless, for what it is worth, some of the list entries are: 164 Retis, 128 Caro-Kanns, 106 King's Indians, 100 Slavs, 96 declined Queen's Gambits, 83 Najdorf Sicilians, 83 Nimzo-Indians, 72 1...e5 Englishes, 66 1...Nf6 Englishes, 59 Queen's Indians, 51 Catalans, 46 1...e6 Englishes, 46 1...c5 Englishes, 44 Berlin Ruy Lopezes, 44 Classical Gruenfelds, and 39 Kan Sicilians.
"... A typical way of choosing an opening repertoire is to copy the openings used by a player one admires. ... However, what is good at world-championship level is not always the best choice at lower levels of play, and it is often a good idea to choose a 'model' who is nearer your own playing strength. ..." - FM Steve Giddins (2008)
What is the strongest opening for white and for black???