The two seem very similar to me. I've been told that there are differences, but I haven't been able to find a summary of what features make it appropriate to use one vs the other to express the possibility of doing something.
Edit: One person said that 到 would be appropriate when it has to do with your physical location. Can anyone elaborate on this?
Edit2: Here's an example: 我看不了电影 vs 我看不到电影.
Your question is about the relationship between potential complement (得/ 不) and the result complement 了 and 到
了 indicates an action is completed
到 indicates an action is successful
在多倫多也吃(得到)正宗川菜 - you can (successfully) find and eat Authentic Sichuan cuisine even in Toronto
在多倫多吃(不到)正宗川菜 - you cannot (successfully) find and eat Authentic Sichuan cuisine in Toronto
我吃得了川菜 - I can eat Sichuan cuisine (and complete it - meaning you can take the spiciness)
我吃不了川菜 - I cannot eat Sichuan cuisine (and complete it- meaning you you can't take the spiciness)
More example:
去到 = go and arrive = successfully went --> 去得到 = able to successfully go --> 去不到 = unable to successfully go
去了 = have gone (it is completed) --> 去不了 = can't go (cannot complete the action)
First to mention that "了" has the following pronunciations - liào,liǎo,le. This answer will concentrate on the latter two.
他自小就聰明的不得了 - He has shown his intelligence/smartness (above and beyond his peers) since a very young age.
她愛玩的不得了 - She loves to play very much (much more than, way beyond, her peers).
她的歌唱的好的不得了 - Her singing is exceedingly good.
Generalize the sentences above, 不得了 is a comment for someone with a trait or performance that is considered unusual when compared to the average people.
Another use of 了 (liǎo) is: 時間太晚了(le), 這電影是看不了(liǎo)了(le) - It is too late for going to watch the movie. Also, 外面在下雨逛街是逛不了(liǎo)了(le). Note in both, the word 了 (liǎo) can be replaced by 成, which means "success", "complete" and "achieve" (note, 成 is a better word for the sentences).
a) - "得了, 別說了." "得了, 別看了." - Enough, stop talk/watch.
b) - "這次我得了一個 A." = "這次我得到一個 A." - This time I got/obtained an A; and "從那裡你得了什麼好處呢?" = "從那裡你得到什麼好處呢?" - What the good thing you got/obtained from there?
Note, in here, both 得了 and 得到 means the same - something you've gotten/obtained in the past
I am not an expert on grammatical terminology. However, I remember reading long ago: a complement is extra information in a sentence, useful, but not necessary.
If you will accept this definition, 得了 and 得到 should perhaps not be called "complements".
That said, I've asked and been told that it is not possible to exchange 得了 in the first 3 sentences for 得到 and vice versa for the second 3 sentences.
我得了很重的感冒。
我得了流感。
他前年得了一枚金牌，大前年得了一枚银牌。
学校扩充未得到许可。
我没有得到道歉之词。
飞机已得到（了）起飞许可。
This is hard to explain, given the fact that the meanings of 得 and 得到 overlap considerably.
Maybe someone here can enlighten us.
As to your examples, they are not examples of 得了 vs 得到:
Depending on the context, these 2 may be the same.
我看不了电影。
I can't watch the film. (because of some problem)
我看不了电影。
I can't see the film. (because of some obstruction)
我看不到电影。
I can't see the film. (because of some obstruction)
