Mix all seeds together in a bowl. Stir in lemon juice and salt.
Cover and leave on counter for at least an hour, allowing seeds to marinate in lemon and salt.
Heat a dry skillet over medium-high heat. Once hot, add the seeds. Pan roast, stirring and turning constantly until fragrant and toasty, about 2-3 minutes.
Transfer hot seeds to a bowl. Add cardamom and maple sugar, stirring well.
Allow mixture to cool completely. Store in an airtight container, preferably in the refrigerator.