Here's the way I think Superman can make around the same or potentially more than The Batman.
Adjusted for inflation opening for recent Superman films + every Gunn CBM :
SUPERMAN RETURNS    80,014,651.60
MAN OF STEEL    154,394,990
GUARDIANS 1    122,880,186
GUARDIANS 2    184,343,206.37
GUARDIANS 3    118,414,021
THE SUICIDE SQUAD    26,205,415
Take the average of that, which would be:  $114,375,411.76
Legs for Gunn's Guardians films.
Guardians 1: 3.54
Guardians 2: 2.66
Guardians 3: 3.03
Average: 3.076666667
And depending on the international/domestic splits, here are a few different scenarios basing on the MoS DOM/INT split and the Guardians films splits:
MAN OF STEEL SPLIT
SUPERMAN (GUARDIANS 1 LEGS)   
    920,202,176    100%
    404,888,958    44%
    515,313,219    56%
    SUPERMAN (GUARDIANS 2 LEGS)   
    691,451,353    100%
    304,238,595    44%
    387,212,758    56%
       
    SUPERMAN (GUARDIANS 3 LEGS)   
    787,630,676    100%
    346,557,498    44%
    441,073,179    56%
    SUPERMAN (AVERAGE LEGS)   
    799,761,402    100%
    351,895,017    44%
    447,866,385    56%
GUARDIANS 1  SPLIT
    SUPERMAN (GUARDIANS 1 LEGS)   
    941,602,227    100%
    404,888,958    43%
    536,713,269    57%
       
    SUPERMAN (GUARDIANS 2 LEGS)   
    707,531,617    100%
    304,238,595    43%
    403,293,022    57%
       
    SUPERMAN (GUARDIANS 3 LEGS)   
    805,947,669    100%
    346,557,498    43%
    459,390,171    57%
       
    SUPERMAN (AVERAGE LEGS)   
    818,360,504    100%
    351,895,017    43%
    466,465,487    57%
GUARDIANS 2 SPLIT
    SUPERMAN (GUARDIANS 1 LEGS)   
    899,753,239    100%
    404,888,958    45%
    494,864,282    55%
       
    SUPERMAN (GUARDIANS 2 LEGS)   
    676,085,767    100%
    304,238,595    45%
    371,847,172    55%
       
    SUPERMAN (GUARDIANS 3 LEGS)   
    770,127,773    100%
    346,557,498    45%
    423,570,275    55%
       
    SUPERMAN (AVERAGE LEGS)   
    781,988,926    100%
    351,895,017    45%
    430,093,909    55%
GUARDIANS 3 SPLIT
    SUPERMAN (GUARDIANS 1 LEGS)   
    964,021,328    100%
    404,888,958    42%
    559,132,370    58%
    SUPERMAN (GUARDIANS 2 LEGS)   
    724,377,608    100%
    304,238,595    42%
    420,139,013    58%
       
    SUPERMAN (GUARDIANS 3 LEGS)   
    825,136,899    100%
    346,557,498    42%
    478,579,402    58%
       
    SUPERMAN (AVERAGE LEGS)   
    837,845,278    100%
    351,895,017    42%
    485,950,261    58%
Average for all those results is: $809,489,028
So yes I think it can make as much and more than The Batman if the marketing plays its cards right and Gunn makes a film as crowd pleasing and four-quadrant as his Guardians films (which I think he will)