I'm from a high school in Ontario, but I'm a US citizen. I don't like to talk badly about my school because I do like it here, but honestly it is pretty bad. There is a 60 percent graduation rate and only 19 percent of graduates end up going to College/University. There are no AP/IB courses available and a lot of violence. I think in the last 20 years only 1 kid from our school ever made it to an ivy league school because it's extremely rare for a student of that caliber to attend our school at all. Around 40 of us end up going to UofT, Mcmaster, Queen's, Waterloo, etc. though. I am academically scoring much higher than any other student, but Im afraid it is still weak in the larger sense. How will my situation look to admissions committees?
The quality of your high school shouldn't detract from your application as long as you have taken advantage of the opportunities that are available to you. Make sure you're enrolled in all the most challenging classes (even if they're not AP or IB). If your school doesn't offer a higher-level class that interests you, look for classes at local community colleges. It sounds like your SAT/ACT scores are already very good, which is awesome. That will go a long way towards improving your chances. If colleges can see standardized evidence of your academic potential apart from your grades, they'll be more likely to consider you for admission.
Students taking challenging courses and achieving high grades are going to get attention, no matter what school name is on the transcript. What teachers and counselors write about the student is significant as well. Individual records, scores, activities, essays, and recommendations all count.
Your application will also be accompanied by a high school profile. This gives colleges statistics on the size of your school, the types of courses offered (they will know you didn't have the opportunity to take AP or IB classes), the grading scale, where students are admitted to college, and more. This ensures that you'll be assessed in the context of your environment, not in direct comparison to someone who went to a fancy shmancy school that offers 30 AP classes and sends ten kids to the Ivy League every year.
Colleges will also sometimes compare you to other people who were admitted from your high school. You can try to find out from your guidance counselor if anyone in past years has been admitted to the schools that interest you. What did that one kid who was admitted to an Ivy League do that was so impressive? It may be that more people haven't been accepted to Ivies from your high school because they simply didn't apply. Sometimes, high-achieving people at low-quality high schools don't apply to top-tier schools as frequently because they think they won't get in or be able to afford the tuition.
You can also read this article for more detailed information about how to navigate the college application process in your specific situation!