"There are a million reasons" means that a person is really passionate about something or someone. To have a million reasons actually means that you cannot list all the reasons, instead you can only say you love something/someone so much that there are too many reasons.

Topic of my Homework: Future Job.

I harbour a dream to of becoming a tourist guide. If someone asks me why, I will instantly answer that there is are a million reasons why I'm passionate about this career. I would love to take people to interesting places and show them all of the hidden beauty of it them.

Besides, I wish to be a person of with many [it would sound more natural to say "a lot of"] acquaintances so because I’m always curious keen/excited/happy to meet new people. It’s not only domestic travelers, but also foreign tourists I like, so I can because I want to appreciate approach different lifestyles. Working as a tourist guide, I will have a chance to expand my horizon, discover new lands, new cultures, luxury architecture, etc.

Since Until then, I got how have to adjust to a new environment and how to adapt to every situation alike. On the other hand, this profession has high demanding requirements and we must be proficient in a lot of fields. Travel is one of my hobbies when since I was a child and becoming a tourist guide is a way I perform to maintain my hobby. I’m really fond of this work and I will be do my best to reach my dream by all any means. 

P.S: And by the way, does could anybody be kind enough to explain for to me this structure: "there is are a million reasons"? I saw it from in the new song of from Selena "The heart wants what it wants" and tried to apply it. Thank you.