Bilingual Marketer, specializing in reaching Latin American and Hispanic audiences both in the US and abroad. I bootstrapped my own solo practice into a full blown digital agency with clients that have included Expedia and Shopify. Ask me about Spanish language marketing, translation, SEO, or Internet Marketing as a whole. If I don't have the answer, then I know someone who does!
I've been helping companies market to Spanish speakers for over 5 years.
As with most questions that stretch across borders and cultures, the answer is, "it depends". Here are some of the factors at play:
1) US Hispanics are over 80% of Mexican descent, meaning that as a general practice, your marketing can be similar
2) But their situations are very different. In the US (according to census data), Hispanics trend lower income. But for products that have a US price point, you are going to have to appeal to wealthier Mexicans (for example).
3) Depending on your product/service, you may have to adapt pricing/messaging to fit cultural norms, or what people can afford.
4) Other issues: if you are a content company that sells advertising, you may want to EXCLUDE people from LATAM, as many advertisers are only trying to sell in the US.
Obviously to give good advice I would need more context. Feel free to set up a call with me (I donate all proceeds to charity), and I'll be glad to talk through this with you.
I can also add value here. First off, you probably don't need hreflang AND canonical, most likely it is one or the other. Second, do the two countries share the same language, or are they different languages? I want to make sure that you actually NEED hreflang, since many sites don't.
Also, I respectfully disagree about building multiple sites (right for some, not for all), especially if you are just starting out. It is best to leverage the SEO efforts that you have already made, and have the second country/language live in a subfolder of your current website.
Let me know if you need more help!