Hi everyone!
I want to major in engineering for undergraduate, but i’ve heard that admissions tend to look at students in engineering more critically.
Plus, there are usually additional supplement essays for engineering that i’d like to avoid.
On the other hand, applying for engineering as compared to undecided allows me to show passion.
Looking for advice. Thanks 
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At colleges where frosh admission selectivity is higher for engineering major applicants, it is typically difficult to change into an engineering major if one enrolls as a non-engineering undeclared student. This is because such colleges usually have engineering majors enrolled to full capacity, so they need to “ration” the space in them, either at frosh admission, or later through a weed-out process (where entering the major requires a GPA significantly higher than that needed to remain in good academic standing and/or a competitive admission process).
You might be able to get away with going in undeclared and moving into the major at a LAC that offers Engineering, but especially at bigger schools (those with full on Schools of Engineering), that could be difficult, as @ucbalumnus says.
Even at liberal arts colleges that offer engineering, it can be incredibly difficult to transfer into the major later; For example, at Lafayette, I was told that in addition to students entering as “engineers” having to meet harsher criteria, engineering majors must declare their major at the end of freshman year, and past that point it is very hard to get into the major.
Colleges are wise to the game of students applying for a less competitive major in terms of admissions and then trying to move into their intended, more competitive major. Most colleges discourage the practice by making internal transfers to a more competitive major very difficult. IMO if you want to be an engineer apply to engineering programs.
http://www.oir.uci.edu/files/adm/IA27-fall-fr-mean-hsgpa-by-major.pdf?R=544517
Just for example: this is UC Irvine data. Engineering school undeclared is admitted at 4.07 and average is 4.09. Physical Sciences school undeclared is admitted at 3.84. But, transfer to engineering as per discussed above will be extremely tough.
Re: #5
UCI lists change of major criteria here: http://www.changeofmajor.uci.edu/
Most engineering majors appear to require a 2.70 GPA overall and 3.00 GPA in major courses.
At every engineering school we visited (larger state schools like A&M, UT, Purdue, etc.) that it is very difficult to transfer into engineering and at one school they flat out told us it was impossible.